This invention relates to a light amount adjusting apparatus which adjusts a light amount on the occasion of projecting an image, which was formed by an image forming unit such as a liquid crystal panel, on a screen, by a projection lens, and a projector which used this.
In general, an apparatus such as a liquid crystal projector, which projects alight image on a screen, is widely used as an apparatus which is connected to imaging devices such as a computer and a television receiver, and projects images which were outputted from these imaging devices, on a screen by a projection lens.
There is such a case that someone feels a light image, which was projected by the suchlike projector, too bright, and dark, depending on a circumstance where it is used. Its cause is, for example, that a person feels light is too bright when an image is made suddenly bright in such a state that pupils of a human, who uses it at a dark place, are opened, and, inversely, at a bright place, a human feels an image placed on a screen is too dark, and so on, and viewability due to brightness of a surrounding becomes a problem.
Consequently, there arises a need to adjust brightness of an image which is projected on a screen, depending on a surrounding environment. In the past, as a method of adjusting the suchlike projection light amount, a method for adjusting a light source which irradiates to a liquid crystal panel etc., and a method for adjusting a voltage which is applied to a liquid crystal panel are known in for example, Patent Document 1 (JP-A-2000-28988 publication).
In the past, as a method for adjusting the suchlike projection light amount (brightness of a screen image), it is known to adjust a voltage which is applied to a liquid crystal panel. However, the liquid crystal panel has a special relation between a voltage and a transmission factor, and there were such problems that it is difficult to control a voltage in such a manner that red, blue and green change evenly on the occasion of changing brightness by changing a voltage, and in addition, a hue also changes on the occasion of adjustment of brightness.
Consequently, it is proposed, in for example, Patent Document 2 (JP-A-2003-121938 publication) etc., to constantly adjust brightness of a screen image by adjusting an amount of light which is projected by a projection lens, by use of a light shielding plate. The Patent Document 2 discloses such a thing that a base member having a projection hole (lens hole) is disposed on a front surface of a projection lens in a direction which is orthogonal to a projection light path of the lens, and a light shielding plate for adjusting a bore diameter of the projection hole larger and smaller (mask member) is attached to this base member, in a direction which is orthogonal to a light path, in such a manner that it can be opened and closed, to adjust a light amount. Therefore, an image, which was formed on a liquid crystal panel, receives light from a light source, and adjusts an image interval on the occasion that it is irradiated on a screen by the projection lens by adjusting an opening of a light path by use of the light shielding plate disposed on a plane which is orthogonal to the projection light, to adjust brightness of the image on the screen.
As above, if it is tried to adjust a light amount by sliding the light shielding plate (mask member), which was disposed on the plane which is orthogonal to the projection light path, as in the above-described Patent Document 2, on the occasion of adjusting a light amount of a light path which is projected by the projection lens, by use of the light shielding plate, it becomes necessary to have a space in which the light shielding member (wing shaped mask plate etc.) goes back and forth and an allocation space of a drive mechanism which opens and closes this light shielding member, on a side portion of the projection lens.
On one hand, a projection lens is normally of a circular shape, and incorporated into a mirror tube section, and therefore, a light amount adjusting apparatus is to be projected to the side of the lens. Therefore, it brought about an undesirable result for miniaturization and space saving of an apparatus. In order to solve the such problems, this invention is such a thing that a pair of light shielding plates (wing members) are disposed on left and right sides of a light path which is projected on a screen by a projection lens, and an opening amount of the light path is adjusted by swinging this light shielding plate in a traveling direction of the light path, and thereby, it was made on the basis of such knowledge that space saving and miniaturization of an apparatus are realized, as compared with such a case that a light shielding plate is configured to be movable back and forth in a plane which is orthogonal to a light path.
However, by adoption of the suchlike configuration, a next problem will newly occur. In sum, as shown in FIG. 11, it is difficult to apply accurate light amount control to a pair of wing members which can be rotated (swung), in a projection light path, in a traveling direction of this light path, due to backlash of a opening and closing mechanism, and in particular, it becomes difficult to carry out light amount adjustment in such a state that the opening of the light path was widely opened. FIG. 11(a) is a state diagram in which the light path was fully opened, and FIG. 11(b) is a state diagram in which the light path was fully closed. Consequently, as compared with such an entrance position that the light path was fully closed (FIG. 11(b)), in case that a light amount adjusting unit 21a, 21b was out of alignment with an angle Φ toward the inside, due to backlash etc., in such a retreat position that the light path was fully opened (FIG. 11(a)), a part of the light amount adjusting unit 21a, 21b gains entry into an inside with position Δ2, and it is impossible to block a light amount to carry out appropriate light amount adjustment. As to this misalignment, for example, in case of assuming that a plate length Lo of the light amount adjusting unit 21a, 21b is 10 mm and misalignment angle Φ is 5 degree, misalignment amount Δ2 becomes approximately 0.87 mm (Δ2=Lo×tan Φ) at the retreat position (FIG. 11(a)), and misalignment amount Δ1 becomes approximately 0.04 mm (Δ1=Lo(1−cos Φ)) at the entrance position (FIG. 11(b)), and misalignment is incomparably large at the fully opened retreat position (FIG. 11(a)), as compared with that at the fully closed entrance position (FIG. 11(b)), and it becomes necessary to eliminate the misalignment at this fully open retreat position (FIG. 11(a)).
The invention has as an object a provision of a light amount adjusting apparatus in which, on the occasion of forming small-size and space saving of an apparatus by swinging a pair of light amount adjusting members, which were disposed at a peripheral side rim portion of a projection light path, there occurs no fluctuation of a light amount, by a dimensional error due to a body difference or backlash of a wing member for use in light amount adjustment, and small-size and space saving of the apparatus is realized and at the same time, light amount adjustment is easy and accurate, and a projector which uses this light amount adjusting apparatus.